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Car pulls when braking

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6.7K views 19 replies 10 participants last post by  amc49  
#1 ·
Hey guys, I know a lot about the mechanics of cars, but diagnosing this one has me a little stumped. I have a 00 focus with 166,000 miles, and just replaced the brakes last sunday. I put quality pads and rotors on, cleaned and lubed all contact points, cleaned the hub with a wire brush, the whole deal. I had a pulsation before I changed the brakes out, and while 95% of the pulsation is gone, that still leaves about 5% pulsation. I also noticed today that under the first few hard stops I made that it makes a slight pull to the left. My alignment is slightly off, but it actually pulls slightly to the right when driving. my rear wheel cylinders are leaking, so its probably not from my rear brakes, as they are likely covered in brake fluid until I replace them in a few weeks. Any ideas?

Thanks!

Matt
 
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#2 ·
Did you bleed the brakes? Also you might want to fix all the problems in the brake system then go from there. Most likely the little bit of pulsation your feeling are the back brakes since they weren't changed. Bleed them and see if it still pulls. You could just need an alignment.
 
#3 ·
I didnt bleed the brakes, they leak the reservoir out in a month or 2 so I am going to get the wheel cylinders, then a flush. I work in a mechanic shop, so I can just throw it on the rack when I finish that. I just wanna know what causes pulls, a hanging piston, air in the lines?

Thanks sleepyboy.

Matt
 
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#5 ·
^^agreed, bleed the brakes. You just did work to the front ones, it doesn't matter if the fluid is leaking from the back. The front and rear lines are seperate from the back. Bleed the fronts sooner than later.
 
#8 ·
if all else fails, check for loose suspension components. inner tie rods can get loose on you and pull in an opposite direction under braking. Does it on my Mazda with a worn itr.
 
#9 ·
How hard is the pull? Air in the system shouldn't cause a pull, just a low/soft pedal.

I am guessing this only presented itself after the brake job correct? If so, I am doubting its any problem with the suspension components, unless something failed immediately after the job.

Does the car have ABS? And did you open the bleeder valve while you pushed the caliper piston into its bore? If not, and you have ABS, hopefully you didn't mess with any of the seals or valves in the valve body. Should always open the bleeder valve on ABS equipped cars when pushing the caliper piston back.
 
#10 ·
yeah it does sound like it was related to the brakes though, and not there before...

ABS systems suck to bleed unless you have the scan tool to actuate it. hopefully not an issue anyway.
 
#11 ·
They only suck if you are installing a new unit that needs to be bled, or you somehow got air into one by letting the master run dry. Otherwise, normal bleeding it shouldn't matter.

Still, to the OP, try bleeding the brakes as suggested above. I don't think its an air problem, but perhaps the action of getting some fluid flow through the system will fix things. Once you are sure they are bled correctly let us know. If the problem is still there, some more in depth diagnosis will be necessary.
 
#14 ·
No abs, front end was tight a thousand miles ago, other than the most minor wheel bearing play. Barely there. In fact, it was replaced 9 months ago and is loose again. Its under warranty at the shop I used to work at, but haven't made the time to bring it in. My old brake pads had life left, but their stopping power was completely shot. I never noticed the pull with the old brakes. I did not open the bleeder screw upon pressing the piston in, I never have in any of my cars, and haven't had an issue. The reservoir runs low (but not dry) every few months. I always add to max when the brake light comes on. Thanks for all your help!

Ps its a very slight pull, but it feels like the LF brake is doing more work than the RF. Stopping power is still very good.

Matt
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#15 · (Edited)
There is a very small notch in the caliper from being worn in, I cleaned best I could with a wire brush, I should probably grind those flush.

EDIT: I am driving to work right now, and was making a U turn at moderate speed, and my left front wheel locked up. Tires are 6 months old and turn couldn't have been.more than 20 mph. Investigate?

Matt
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#16 ·
Hey guys, update. I got the time to bring my car in and rotate the tires, and double check everything on the brakes. The slide bolts were very difficult to move in and out, so I polished away all the old grime and grease, cleaned the bolt holes, grinded the caliper slides, grinded the wheel hub/ disc surface, washed the rotors with soap and water, and reassembled. the brakes certainly clamp more quickly and smoothly, and they return much better (so the car feels like it has less drag).

Here is the problem. It still pulsates, and still pulls to the left, basically as hard as before. I probably need to balance my tires, but I was shocked to see it still doing the same thing. however, overall braking performance has increased now that they clamp much smoother.

Matt
 
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#17 ·
More updates.

I took my rotors and pads off to get a warranty replacement. The pads ended up being a lower grade than what I had purchased and were in the wrong packaging, so I just stuck with my original pads. I just really want to get rid of the pulsation. New rotors fit perfectly flush to the hub, regreased everything.

Still pulsates and pulls to the left.

I got a one man brake bleeder kit and bled the front out, still all the same. The left rotor appeared more worn than the passenger. Wtf else do I need to do?

Vehicle was aligned last week.

Matt
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L
#19 ·
ok guys heres another thing that nobody has mentioned and that is that front wheel drive cars have DIAGONAL BRAKING. Half the master cylinder does the left front wheel and the right rear wheel. And the othr half of the master does the other two wheels. Get it? So if you have a bad master cylinder, you are possibly not getting very much line pressure to one of the front wheels and getting normal line pressure to the other one, therefore it pulls when braking! TA DA! Hi pressure brake pressure gauges are used to diagnose problems like this, although not often used, they are what you need to do next. Compare lf pressure to rf pressure. Correct as necessary. Act accordingly. You are welcome.
 
A
#20 ·
Uh, NO. Why do you think the factory did that if it is not safe?

If only one brake works and say it's right front, when you brake the car will pull to the right and even try to spin out in that direction if you brake hard enough. Add the left REAR brake and it neutralizes that tendency to spin so long as you are not roadracing the car. The rear drag on the opposite side cancels a lot of the spin out physics.
 
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